Final answer:
The physiological feature of the infant brain that allows drugs to enter the brain is the immature blood-brain barrier (BBB).
Step-by-step explanation:
The physiological feature of the brain of an infant that allows drugs to enter the brain that normally would be blocked in an adult patient is the immature blood-brain barrier (BBB). The BBB is a physiological barrier that restricts the entry of substances from circulating blood into the central nervous system (CNS). In infants, the BBB is not fully developed, allowing certain drugs to pass through more easily.
During fetal development, the BBB is not fully functional, allowing some substances to pass through and reach the developing brain. However, as the infant grows and develops, the BBB becomes more mature and restrictive, limiting the passage of drugs and other substances into the brain.
This difference in BBB development between infants and adults is an important consideration in pharmacokinetics and drug delivery to the CNS.